public class Test09 {
    /**
     * 给定两个整数数组preorder 和 inorder，其
     * 中preorder 是二叉树的先序遍历， inorder是同一棵树的中序遍历，
     * 请构造二叉树并返回其根节点
     *
     *
     */
    class TreeNode {
        public int val;
        public TreeNode left;
        public TreeNode right;
        public TreeNode() {}
        public TreeNode(int val) {
            this.val = val;
        }
        public TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }
    public int i = 0;
    public TreeNode buildTree(int[] preorder, int[] inorder) {

        return buildTreeChild(preorder,inorder,0,inorder.length-1);
    }

    public TreeNode buildTreeChild(int[] preorder, int[] inorder,
                                   int inbegin,int inend) {
        if(inbegin > inend) {
            return null;
        }
        TreeNode root = new TreeNode(preorder[i]);
        //找到当前根，在中序遍历的位置
        int rootIndex = findIndex(inorder,inbegin,inend,preorder[i]);
        i++;
        root.left = buildTreeChild(preorder,inorder,inbegin,rootIndex-1);
        root.right = buildTreeChild(preorder,inorder,rootIndex+1,inend);
        return root;
    }

    private int findIndex( int[] inorder,int inbegin,int inend, int key) {
        for(int i = inbegin;i <= inend; i++) {
            if(inorder[i] == key) {
                return i;
            }
        }
        return -1;
    }
}
